The iBiquity Digital Corporation HD Radio™ system is designed to permit a smooth evolution from current analog amplitude modulation (AM) and frequency modulation (FM) radio to a fully digital in-band on-channel (IBOC) system. This system delivers digital audio and data services to mobile, portable, and fixed receivers from terrestrial transmitters in the existing medium frequency (MF) and very high frequency (VHF) radio bands.
IBOC signals can be transmitted in a hybrid format including an analog modulated carrier in combination with a plurality of digitally modulated subcarriers, or in an all-digital format wherein the analog modulated carrier is not used. Using the hybrid format, broadcasters may continue to transmit analog AM and FM simultaneously with higher-quality and more robust digital signals, allowing themselves and their listeners to convert from analog to digital radio while maintaining their current frequency allocations. IBOC hybrid and all-digital waveforms are described in U.S. Pat. No. 7,933,368, which is hereby incorporated by reference.
Channel State Information (CSI) is useful in the decoding of digital signals in radio receivers. CSI as a signal-to-noise ratio (SNR) conveys the reliability of the associated digital symbols; while the estimation of channel gain, magnitude, and phase allows the demodulator to remove or compensate for them. Accurate and timely CSI estimation is important to maximize reliable decoding performance.
It is desirable to improve the accuracy and timeliness of the CSI estimation for HD Radio receivers.